The objective of this project is to define mechanisms controlling the selective expression on skin homing T-cells of the epidermotrophic T cell chemokine receptor CCR10, and to characterize the role of sunlight (uvb) and Vitamin D in this process. Our aims are: 1. To confirm the ability of cutaneous dendritic cells to support Vitamin D3 induces T-cell CCR10 expression. Langerhans cells and cutaneous DC will be accessed for expression of CYP27A1 and, B1;ability to process D3 to 1,25OH D3 in T cell cocultures;and to support Vitamin D3 induction of T cell CCR10. 2. To determine whether Vitamin D induction of CCR10 in vitro or in vivo is mediated by the canonical Vitamin D Receptor (VDR), and if the VDR directly interacts with the CCR10 promoter. VDR-/- mice will be assessed for ability to express T cell CCR10 upon activation in the presence or absence of 1,25 D3, or in vivo. Direct binding assays will determine whether the VDR binds in a ligand-dependent fashion to the putative VDRE present in the CCR10 promoter region. 3. Define the relative ability of uvb-induced vs. dietary Vitamin D to induce T cell CCR10 expression in vivo. The role of uvb-generated D3 on CCR10 expression by T cells in skin draining LN will be assessed, and compared with the effects of dietary Vitamin D. 4. To test the hypothesis that RAR and VDR agonists (retinoic acid vs. 1,25 Vitamin D) act competitively, inhibiting induction of CCR10 or of gut homing receptors respectively, thus reinforcing the specificity of epidermotrophic vs. gut homing receptor expression. The effects of retinoic acid on Vitamin D3 induced CCR10 expression, and of 1,25 D3 on RA induced gut homing properties, will be measured in vitro T cell activation assays. 5. To assess the requirement for IL12 signaling for Vitamin D induced CCR10 induction in vivo. Preliminary results show that IL12 potentiates and enables the T cell epidermotrophic response to Vitamin D3. Gene targeted mice will be used to assess the requirement for IL12 signaling, and the potential for other cytokine involvement in this process. This proposal addresses the mechanisms that segregate target effectors and proliferative components of immune memory to cutaneous antigens. This problem has importance to a basic understanding of tissue- specific immune responses, but also to the specialized immune and inflammatory pathologies associated with skin such as psoriasis, DTH reactions and bullous diseases.